1. Field of the Invention
The present invention relates to a wireless power feeder, wireless power receiver and wireless power transmission system for transmitting power by a non-contact method.
2. Related Background Art
Japanese Patent Application Publication No. 2010-233442 discloses a wireless power transmission system for transmitting power from a wireless power feeder to a wireless power receiver by a non-contact method (wirelessly). In this wireless power transmission system, a wireless power feeder 1 and wireless power receiver 2 have a power feed resonance circuit 12 and power receive resonance circuit 21, respectively, wherein non-contact power transmission is carried out using a magnetic field resonance effect between the power feed resonance circuit 12 and the power receive resonance circuit 21.
In this type of wireless power transmission system, when, for example, the relative distance between the power feed resonance circuit 12 and the power receive resonance circuit 21 changes, the state of coupling between the power feed resonance circuit 12 and the power receive resonance circuit 21 changes, lowering the power transmission efficiency.
In this regard, Japanese Patent Application Publication No. 2010-233442 discloses an invention which detects an impedance observed from a power feeder side, and sets; in accordance with the absolute value or the phase of the detected impedance, a frequency of an AC power fed to the power feed resonance circuit 12. The wireless power feeder 1 has an oscillator 11 for inputting the AC power to the power feed resonance circuit 12, an impedance detecting apparatus 4 for detecting the impedance observed from the power feeder side within a predetermined frequency range, and a frequency varying apparatus 3 for setting the frequency of the AC power input to the power feed resonance circuit 12, in accordance with the absolute value or the phase of the detected impedance. Therefore, the lowering of the power transmission efficiency can be prevented even when the state of coupling between the power feed resonance circuit 12 and the power receive resonance circuit 21 changes.
Note that the wireless power receiver 2 disclosed in Japanese Patent Application Publication No. 2010-233442 has a load coil 212 (power receive load coil 212), and a power receive coil 211 of the power receive resonance circuit 21 is connected to a load 5 through electromagnetic coupling with the power receive load coil 212. As a result, a change in a self-resonance frequency of the power receive resonance circuit 21 resulting from the effect of the load can be prevented.